2,084 research outputs found
A three-dimensional wavelet based multifractal method : about the need of revisiting the multifractal description of turbulence dissipation data
We generalize the wavelet transform modulus maxima (WTMM) method to
multifractal analysis of 3D random fields. This method is calibrated on
synthetic 3D monofractal fractional Brownian fields and on 3D multifractal
singular cascade measures as well as their random function counterpart obtained
by fractional integration. Then we apply the 3D WTMM method to the dissipation
field issue from 3D isotropic turbulence simulations. We comment on the need to
revisiting previous box-counting analysis which have failed to estimate
correctly the corresponding multifractal spectra because of their intrinsic
inability to master non-conservative singular cascade measures.Comment: 5 pages, 3figures, submitted to Phys. Rev. Let
Emergence of log-normal type distributions in avalanche processes in living systems : a network model
Funding We acknowledge financial support from the Agence Nationale de la Recherche (ANR grant number ANR-18-CE45-0012-01) and from the French Research Minister (MESRI) for SP. PhD funding. Acknowledgments We are very grateful for the participants of the second ISINP meeting at Lake Como for stimulating exchanges about our talk. We are thanful to P. Argoul, A. Guillet, E. HartĂš, L. Delmarre for fruitful discussions. SP wishes to thank T. Matteuzzi for his inspiring considerations. We are indebted to Erika Polizzi for her graphical help.Peer reviewedPublisher PD
Power-law and log-normal avalanche size statistics in random growth processes
ACKNOWLEDGMENTS We thank J.P. Bouchaud for constructive comments. We acknowledge financial support from the Agence Nationale de la Recherche (ANR grant number ANR-18- CE45-0012-01) and from the French Research Ministry (MESR) (contract No. 2017-SG-D-09) and from ENS Lyon for SP PhD funding. FJPR acknowledges financial support from the Carnegie Trust.Peer reviewedPostprin
Structural organization of human replication timing domains
AbstractRecent analysis of genome-wide epigenetic modification data, mean replication timing (MRT) profiles and chromosome conformation data in mammals have provided increasing evidence that flexibility in replication origin usage is regulated locally by the epigenetic landscape and over larger genomic distances by the 3D chromatin architecture. Here, we review the recent results establishing some link between replication domains and chromatin structural domains in pluripotent and various differentiated cell types in human. We reconcile the originally proposed dichotomic picture of early and late constant timing regions that replicate by multiple rather synchronous origins in separated nuclear compartments of open and closed chromatins, with the U-shaped MRT domains bordered by âmasterâ replication origins specified by a localized (âŒ200â300kb) zone of open and transcriptionally active chromatin from which a replication wave likely initiates and propagates toward the domain center via a cascade of origin firing. We discuss the relationships between these MRT domains, topologically associated domains and lamina-associated domains. This review sheds a new light on the epigenetically regulated global chromatin reorganization that underlies the loss of pluripotency and the determination of differentiation properties
Automated Detection of Coronal Loops using a Wavelet Transform Modulus Maxima Method
We propose and test a wavelet transform modulus maxima method for the au-
tomated detection and extraction of coronal loops in extreme ultraviolet images
of the solar corona. This method decomposes an image into a number of size
scales and tracks enhanced power along each ridge corresponding to a coronal
loop at each scale. We compare the results across scales and suggest the
optimum set of parameters to maximise completeness while minimising detection
of noise. For a test coronal image, we compare the global statistics (e.g.,
number of loops at each length) to previous automated coronal-loop detection
algorithms
Analysis of fine-scale mammalian evolutionary breakpoints provides new insight into their relation to genome organisation
<p>Abstract</p> <p>Background</p> <p>The Intergenic Breakage Model, which is the current model of structural genome evolution, considers that evolutionary rearrangement breakages happen with a uniform propensity along the genome but are selected against in genes, their regulatory regions and in-between. However, a growing body of evidence shows that there exists regions along mammalian genomes that present a high susceptibility to breakage. We reconsidered this question taking advantage of a recently published methodology for the precise detection of rearrangement breakpoints based on pairwise genome comparisons.</p> <p>Results</p> <p>We applied this methodology between the genome of human and those of five sequenced eutherian mammals which allowed us to delineate evolutionary breakpoint regions along the human genome with a finer resolution (median size 26.6 kb) than obtained before. We investigated the distribution of these breakpoints with respect to genome organisation into domains of different activity. In agreement with the Intergenic Breakage Model, we observed that breakpoints are under-represented in genes. Surprisingly however, the density of breakpoints in small intergenes (1 per Mb) appears significantly higher than in gene deserts (0.1 per Mb).</p> <p>More generally, we found a heterogeneous distribution of breakpoints that follows the organisation of the genome into isochores (breakpoints are more frequent in GC-rich regions). We then discuss the hypothesis that regions with an enhanced susceptibility to breakage correspond to regions of high transcriptional activity and replication initiation.</p> <p>Conclusion</p> <p>We propose a model to describe the heterogeneous distribution of evolutionary breakpoints along human chromosomes that combines natural selection and a mutational bias linked to local open chromatin state.</p
Wavelet-based multifractal analysis of dynamic infrared thermograms to assist in early breast cancer diagnosis
Breast cancer is the most common type of cancer among women and despite recent advances in the medical field, there are still some inherent limitations in the currently used screening techniques. The radiological interpretation of screening X-ray mammograms often leads to over-diagnosis and, as a consequence, to unnecessary traumatic and painful biopsies. Here we propose a computer-aided multifractal analysis of dynamic infrared (IR) imaging as an efficient method for identifying women with risk of breast cancer. Using a wavelet-based multi-scale method to analyze the temporal fluctuations of breast skin temperature collected from a panel of patients with diagnosed breast cancer and some female volunteers with healthy breasts, we show that the multifractal complexity of temperature fluctuations observed in healthy breasts is lost in mammary glands with malignant tumor. Besides potential clinical impact, these results open new perspectives in the investigation of physiological changes that may precede anatomical alterations in breast cancer development
La transformation en ondelettes continue : un microscope mathématique adapté à l'étude des propriétés d'invariance d'échelle et de corrélations à longue portée des séquences d'ADN
Depuis le dĂ©but des annĂ©es 90, l'intĂ©rĂȘt des mathĂ©maticiens, physiciens et informaticiens pour l'analyse statistique des sĂ©quences d'ADN n'a pas cessĂ© de croĂźtre. En effet, les immenses progrĂšs de la biologie molĂ©culaire et les grands projets de sĂ©quençage ont rĂ©vĂ©lĂ© l'extraordinaire complexitĂ© des gĂ©nomes. Afin de mieux comprendre l'organisation et l'Ă©volution des gĂ©nomes, il est apparu nĂ©cessaire d'introduire de nouveaux concepts et de nouvelles techniques d'analyse du signal. Ainsi la possibilitĂ© que les sĂ©quences d'ADN prĂ©sentent des propriĂ©tĂ©s d'invariance d'Ă©chelle associĂ©es Ă l'existence de corrĂ©lations Ă longue portĂ©e (CLP) a Ă©tĂ© le sujet d'une longue controverse. La raison principale de ce malentendu est le caractĂšre non stationnaire des sĂ©quences d'ADN rĂ©sultant de l'hĂ©tĂ©rogĂ©nĂ©itĂ© de composition des gĂ©nomes. Cette observation nous a conduit Ă proposer l'utilisation de la transformation en ondelettes continue (TO) comme outil naturel d'analyse des sĂ©quences d'ADN : par un choix adĂ©quat de l'ondelette analysatrice, on peut s'affranchir de la "structure mosaĂŻque" de ces sĂ©quences et quantifier l'existence de CLP associĂ©es Ă des propriĂ©tĂ©s d'invariance d'Ă©chelle monofractales. L'exploration de sĂ©quences d'ADN du gĂ©nome humain sous l'optique du microscope TO, nous a permis de dĂ©montrer l'existence de CLP dans les sĂ©quences exoniques (codantes pour les protĂ©ines) comme dans les sĂ©quences introniques (non codantes), remettant par lĂ en cause les diffĂ©rentes interprĂ©tations de ces corrĂ©lations Ă l'aide de modĂšles de dynamique Ă©volutive (plasticitĂ©) des gĂ©nomes. En profitant de la disponibilitĂ© de gĂ©nomes complets (levure, E. coli,...) et en utilisant diffĂ©rentes tables expĂ©rimentales associant des di- ou tri- nuclĂ©otides Ă des grandeurs de nature structurelle (courbure, flexibilitĂ©), nous avons montrĂ© rĂ©cemment qu'il est possible d'extraire des sĂ©quences d'ADN des informations sur l'organisation spatiale et dynamique de la double hĂ©lice dans les cellules via l'interaction avec certaines protĂ©ines de structure telles que les histones pour la formation du nuclĂ©osome eucaryote. En particulier, l'existence et la nature des CLP jusqu'Ă des distances de l'ordre de 3 104 nuclĂ©otides dans certains profils de courbure et/ou de flexibilitĂ© locales permettent de diagnostiquer la prĂ©sence de nuclĂ©osomes dans les gĂ©nomes Ă©tudiĂ©s. L'observation de certaines CLP dans tous les organismes eucaryotes ainsi que dans les organismes des deux autres rĂšgnes (eubactĂ©ries et archaeabactĂ©ries) suggĂšre fortement que ces corrĂ©lations pourraient ĂȘtre essentielles aux phĂ©nomĂšnes de condensation-dĂ©condensation de la chromatine en relation avec les processus de rĂ©plication, transcription et division cellulaire
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